The present invention relates to paper feeding in printer and particularly to the transport of single sheets as well as continuous endless sheet feeding particularly, into a matrix printer which printer includes a printing platen and friction rollers with an additional feature of providing a traction device for endless sheet feeding.
Generally speaking, the paper transport device in a matrix printer must be adapted to feed into the printer single sheets, on an individual basis, but it must also be equipped for continuous sheet feeding that is to say it must also feed endless sheets having for example, special perforations along the margin. For this, one provides usually a tractor downstream from the printing area, to pull the endless sheet through the printer. The initial threading of the individual sheets as well as the endless sheets, the merging of the feed channels and subsequent processing that includes printing in a continuous mode or by step by step advance has to be carried out without incurring problems such as paper bunching and other interference. Compounded is the problem by the fact that for example, the individual sheets or the endless sheet may have, at times, different formats. Known here is, for example, the special requirement for ticket printing such as the printing of airline tickets or the printing of checks, of customer's receipts, of labels and so forth.
The feeding, printing and removal of such print stock, be it individual sheets or an endless sheet, moreover, does pose a variety of specific problems. For example, depending upon the position of the drives in the beginning, it may be require to waste certain amount of paper and to pass through the system, at first, an empty page or some empty sheets or parts thereof. Another problem is that the drives may cause the paper to bulge or bunch for a variety of reasons, the paper is longer taut all the way through and that, in turn, can lead to bunching and ultimately to just stopping of the printer. More recently, another requirement has been added to the paper transport device in such a printer, namely the possibility of retracting the paper if, for some reason, it is discovered that the wrong kind has been used and a different type or kind of paper should be used instead. Thus, ripping the wrong sheets out of the printer is not only primitive but wasteful but ultimately may add to down time.